What you are seeing is just a material. You need to spawn an actual grid on top of your terrain (or made up of chunks of your terrain in blocks or something). You could just use a flat plane mesh that you make invisible with a material. That way you can detect collision, mouse clicks that sort of thing and get a reference to the actor. Click on a tile and you can call a function within that tile to spawn a building of some type on it. Or maybe the tile returns false or something if you can’t interact with it.